ODC-MEDIATED BIOSYNTHESIS AND DAO-MEDIATED CATABOLISM OF PUTRESCINE INVOLVED IN ROOTING OF CHRYSANTHEMUM EXPLANTS IN-VITRO

Foliar discs (8 mm diameter) from expanding leaves of the middle part of vegetative shoots of Chrysanthemum morifolium Ramat raised in vitro , rooted on their basal side from the 6th day when cultured in vitro o n a Murashige and Skoog medium containing indolylacetic acid (1 mg l(- 1)). Measurements (every two days) of free putrescine indicated a cont inuous level increase from the beginning. Conjugated polyamines (75% i n the hydroxycinnamoyl form) raised from zero at the beginning of cult ure to peak at day 4. No ODC (ornithine decarboxylase) or ADC (arginin e decarboxylase) activity was detected at day 0 but a high activity of both enzymes was measured at day 2 (ODC > ADC); it declined afterward s. DFMA (alpha-difluoromethylarginine), an inhibitor of ADC,when incor porated in the rooting medium from time 0 (10(-3) M), inhibited comple tely ADC activity, but reduced the level of free putrescine by only 25 % in the leaf explants without affecting the conjugated pool, and it h ad no effect on rooting. DFMO (alpha-difluoromethylornithine), an inhi bitor of ODC at the same concentration, completely inhibited ODC activ ity with a reduction of putrescine accumulation and a total inhibition of the formation of polyamine conjugates. Root formation was totally inhibited by DFMO alone. A simultaneous application of putrescine (10( -3) M) to DFMO restored complete rooting. There was no DAO (diamine ox idase) activity at day 0 in the foliar explants but it increased rapid ly to a maximum at day 2 on the rooting medium. PAO (polyamine oxidase ) activity did not undergo such a variation. No DAO activity was measu red in explants on the root- non forming medium containing DFMO. beta- OH hydrazine, an inhibitor of DAO, inhibited the development of activi ty of this enzyme in the leaf explants on the rooting medium. Putresci ne and its conjugate accumulated in such treated explants. Rooting was completely inhibited in the presence of beta-OH hydrazine but callus grew around the disc. Such a callus did not develop in the presence of DFMO. The results thus pointed to the involvement of ODC mediated bio synthesis and DAO-mediated catabolism of putrescine in the induction o f rooting of this material.